Biaxially oriented polyester films are used for a variety of purposes including packaging, industrial, electronic, decorative, label, and imaging applications and often perform multiple functions. For example, biaxially oriented PET films and laminations are popular, high performing, and cost-effective flexible substrates for a variety of film structures used in thermal transfer printing, such as transferring ink to substrates by thermal sublimation.
These films may, for example, be used as a thermal transfer ribbon. The films, for example, may be used in the printing of barcodes or digital photographs on paper or other suitable recipient substrate.
Thermal transfer printing applies to printing processes that utilize heat in order to produce an image by either physical or chemical means or a combination of both (G. Laporte et al., “The Forensic Analysis of Thermal Transfer Printing”, J. Forensic Science, Vol. 48, No. 5 (2003)). Its predominance has evolved in the past three decades with the advent of bar coding, retailer receipts, fax machines, event tickets, high resolution digital photography and plastic identification cards.
Thermal transfer printing is a digital printing process in which material is applied to paper (or some other material) by melting a coating of ribbon so that it stays glued to the material on which the print is applied. In its simplest form the ribbon is formed from a polymeric substrate and at least one layer of ink coating. As the ribbon moves over the print head, resistive elements on the print head get heated, this causes the ink to melt. As the ink becomes molten, it releases from the substrate film and transfers onto the receiver (print surface). Release happens either via ink sublimation (“dye diffusion thermal transfer” D2T2) or by means of a wax carrier (“thermal mass transfer, TMT). The used ribbon separates from the receiver and is wound up on a take-up spindle.
Embodiments of a substrate composite film for thermal transfer printing may include a biaxially oriented base layer including polyester and lubricant particles. Embodiments of a film structure for thermal transfer printing may include a biaxially oriented base film including polyester, and lubricant particles, an adhesive layer on a surface of the biaxially oriented base layer; a colored dye coating on the adhesive layer; and a low friction coating on a surface of the biaxially oriented base layer opposite the adhesive layer.
Previous thermoplastic films for thermal transfer printing were often difficult to wind because of bad air exclusion performance on the role. For example, JP-2008-246683 describes a biaxially oriented polyester film for a sublimation-type thermosensitive image transfer recording material obtained by applying a coating solution to at least one side of a polyester film and stretching the resulting film. The describe films include large particles in small amounts, which can result in bad air exclusion when rolled.